Liquid-phase reaction kinetics includes the study of the process of chemical reactions in liquids. Much of the chemistry occurs in sub-millisecond time-scales. Many biological processes such as cell activation, enzyme reactions, and protein folding also require sub-millisecond analysis to investigate intermediate states formed during the reaction. Reactants are often mixed to initiate the chemical reaction.
For example, liquid reactants A and B are mixed to produce product C. The initiation point of this reaction is when the reactants A and B come in contact with one another. The reactants A and B can be mixed together by a mixer. The reactants A and B are allowed to react for a defined duration called the delay. After the delay, the reaction can be quenched by adding reaction inhibitor D. The stopping point of this reaction is when the reactants A and B come in contact with reaction inhibitor D. The reactants A, B, product C and inhibitor D are all mixed together.
Both the initiation point and stopping point may not be instantaneous in a practical mixer. A certain length of time is generally required for the substances in the reaction to adequately mix together. This length of time between the first point of encounter and the point when the substances are completely mixed is called the dead time.
Reduction of dead time better defines the initiation point and stopping point of the chemical reaction. Control of the reaction time by varying the delay is desirable. The delay is the time after the initiation point and before the stopping point, during which the reactants A and B react to produce C. The product C is then collected for further analysis. A high speed mixer apparatus that allows varying delay times and continuous product collection is desired.
Most chemical analysis protocols prefer sub-millisecond mixers that allow short delay times, if the reaction rate is fast, e.g., having sub-millisecond reaction time constants.
Some conventional mixers that allow millisecond mixing are available.
One such mixer is the Berger ball mixer. The fluids to be mixed are injected onto a ball. The flow velocity at which the fluid streams are injected onto the ball drives the fluids around the ball. The flow of the different fluid streams around the curved surface of the ball causes turbulence. Mixing rates can be increased by increasing the flow velocity of the injected fluids thereby increasing the turbulence experienced by the fluids. Berger ball mixers can be implemented in computer controlled fluid delivery systems such as the BioLogic SFM4/Q Quenchflow, available from Molecular Kinetics, WA. These setups can have dimensions of 1 in.times.0.5 in.times.0.5 in.
One undesirable feature of some Berger ball mixer setups is additional dead volume. Dead volume is the volume the liquid sample occupies in an apparatus. If mixers are not integrated, the reactants are transferred from one mixer to the other the volume that is taken up during the transfer adds to the total dead volume.
The Berger ball mixer setups are relatively large devices that typically allow reaction delay times of around 3 ms. Any significant delay shorter than 3 ms are usually not attainable.
Mixing using multicapillaries and free jet mixing has also been demonstrated. These methods are not usually adapted for use for a second quench after the first mixing. The capability of a second quench and/or subsequent mixing steps are sometimes desired for studying reaction intermediate states.
Chemical analysis sometimes require the ability to stop the reaction and thus "freeze" the chemical state of the reactants in time. An apparatus that can "freeze" the chemical state of the reactants after a controlled delay is desired.
In the micro-electromechanical systems ("MEMS") field, micro-mixing devices fabricated have operated in low Reynolds numbers, e.g. less than 2000. Low Reynolds numbers regimes results in mixing times on the order of seconds.